**3. Nanoparticles and their action on plants**

The nanotechnology application in agriculture is for our world one of the most important domains of study due to the possibility of increasing for different culture production and assisted plant protection against pests and diseases together with the monitoring of pathogenic agents. In this regard, the application of nanotechnology in the control of crop yield and crop protection is relatively recent compared to organic or chemical nutrients and different drug delivery or pharmaceuticals [31, 32].

One of the most important nutrients for humans and plants is iron (Fe) where iron deficiency is common in nowadays human diet affecting over 2 billion people

**57**

*Application of Nanotechnology Solutions in Plants Fertilization*

in the world [33] Iron is essential for plant development and plays an important part in photosynthetic process being implied in redox reaction as well as generating reactive oxygen species [34]. Due to its properties iron containing nanoparticles have been used as nano-fertilizer for nutrition of plants. As an example there was observed [35] a positive effect of nano-FeO and nano-ZnCuFe oxide on the growth of mung (*Vigna radiata)* seedling, as well a positive influence on leaf and pod dry weight on soybean yield and quality [36]. The problem of high rate of accumulation of iron oxide nanoparticles in plants that conduced to precipitation in gravitational field can be solve by surface-coating materials [37], a promising way to improve the agronomic traits. Surface iron coating materials as nano-Fe2O3 coordinated with humic acid improved the mobility of iron in peanuts [38] or water-based ferrofluids stabilized with citric acid on the growth of maize [39]. In this spirit, in literature [40] there are data regarding the action of nono-iron fertilizer capped with ethylenediaminetetra acetic acid (EDTA) upon sunflower(*Helianthus annuus)* by foliar and soil application. An important parameter in studying the functional biology is plant biomass, in this regard the effect of applied nano-fertilizer by foliar treatment is the improving of aerial organ dry biomass while the effect on soil application of nano-Fe-EDTA is not conclusive. Regarding aerial organ fresh biomass both foliar and soil addition of nano-Fe-EDTA had the effect of increasing aerial organ fresh weight of the plants as compared to classic fertilizer. In this method of applying nano-Fe-EDTA there exists an increasing of leaves number in percentage by 21.42% as compared to control plants [40]. As regards, the plant height the application of nano-Fe-EDTA is effective also in foliar and soil treatment and taking into account these experiments the general growth of sunflower is influenced by iron oxide nanoparticles. The nano-fertilizer that treated the plan influenced also the physiological parameters in the sense that all treated plants had a higher chlorophyll content, the most important pigment, level than the test plants i.e. from the total level of 2.69 mg/g and 2.34 mg/g belongs to chlorophyll to the treated plants with nano-Fe-EDTA through soil absorption, indicated the translocation of coated nanoparticles from roots to the aerial parts. This treatment method implied penetration points on the leave surface i.e. stomata and subestomatic chambers which means hydrophobic penetration of nanoparticles through these pores. Another problem for foliar application of nanoparticles is the possibility for their accumulation in cells from epidermis of petiole near the application point limiting in this way their possible contribution to plant growth or photosynthesis reaction. However, the effect of an organic shell around nano-Fe made these nanoparticles more compatible for entering and translocation in the plant [40]. Another direction to suppress iron deficiency common in human diet is to use iron fertilizers based on humic substances extracted from lignites, such as leordine, it is stated [41] that this kind of fertilizer is more ecofriendly than synthetic iron chelates as discussed above, but they are less efficient in suppressing iron chlorosis. Low concentrations of superparamagnetic Fe-nanoparticles increased significantly the chlorophyll contents in sub-apical leaves of soybeans under hydroponic conditions. The plants fertilized with the leonardite humates accumulated slightly higher fresh weight than those fertilized with the iron chelate, the humic substances generally increase the shoot and root growth by 15–25% and the accumulation of total iron in pods for soybean plants reaches 50 mg/kg under conditions of sufficient nourishment [41]. The applied nanoparticles of Fe57 were capable to supply the Fe57 deficiency in plant and it was transported from root to shoot and reaches the pods, this iron humate was prepared taking into account its maximum complexing capacity in order to avoid the iron flocculation in calcareous conditions [41]. As a remark, in the context of sustainable agriculture, the Fe-nanoparticles can be considered as a part of novel

technology in line with the politics of precision and sustainable agriculture.

*DOI: http://dx.doi.org/10.5772/intechopen.91240*

## *Application of Nanotechnology Solutions in Plants Fertilization DOI: http://dx.doi.org/10.5772/intechopen.91240*

*Urban Horticulture - Necessity of the Future*

intense process related to a higher ion release on the increased nanoparticle surface area [27]. It is worth to mention that the problem of *in planta* translocation, i.e. the way that the foliar application of nanoscale nutrients affects root pathogens, is still under research in the sense that pathogens can be released after shoot-root transfer or the induced host resistance. A non-classical nutrient besides metal and metaloxides there is based on carbon nanomaterials in the forms of C60/70 fullerenes, carbon nanoparticles, or single/multiple wall carbon nanotubes (SWCNT/MWCNT). An extended study [11] in literature upon the action of MWCNT, SWCNT, graphene and bulk activated carbon onto tomato plants grown in artificial medium revealed an enhancement of biomass by stimulating the growth. The molecular analysis upon the action of MWCNT has shown a stimulation of cell division and plant growth due to the activation of water channels (aquaporins) and regulatory genes for cell division and extension. Carbon nanomaterials exposure can alter the different co-existing organic contaminants in various kinds of soils. In this regards, carbon nanomaterials presents toxicity to soil microorganisms, with accent to SWCNT including fungal community. Carbon nanomaterials have potential to enhance plant growth, nutrient uptake, seed germination or fruit yield the most promising one being MWCNT with positive effects on different crop species. The large inters in the use of nanomaterials is based on the increase global production of nanomaterials and their possible application in agriculture with hazards and risks to be investigated. An exposed [28, 29] "realistic exposure scenario" for TiO2, Ag and carbon nanotubes proposed the doses of 0.4, 0.02 and 0.01 μg/kg/year although the relationship between these values and the actual concentration in the environment

It is worth to mention, that in general the discussion to nanomaterials in agriculture refers also to a most prominent fraction of nanomaterials that are non-solids comprising nanoscale structures that can encapsulate an active ingredient in plan protection product. Generally active substances have poor solubility in water and at room temperature are brought to solution with organic (co)solvents. In order to avoid the use of organic (co)solvents one solution is stated [30] the use of oil/water emulsions. Generally the physical appearance of non-solid nanomaterials are lipid base in liposomes, micelles or cochleates, in polymer based in micelles, nanosphere, nanocapsules and polymersomes or in emulsions base as liquid crystals and microemulsions. The nanomaterials in non-solid forms enhance the solubility and the coverage of the hydrophobic leaf surface together with the penetration of the active

As presented, the characteristics of solid and non-solid nanomaterials have been investigated in the last decade in order to understand the effect of nanonutrients in culture fertilization as well as in plant protection with promising results together with various studies regarding the toxicity of nanoparticles in the environment.

The nanotechnology application in agriculture is for our world one of the most important domains of study due to the possibility of increasing for different culture production and assisted plant protection against pests and diseases together with the monitoring of pathogenic agents. In this regard, the application of nanotechnology in the control of crop yield and crop protection is relatively recent compared to organic or chemical nutrients and different drug delivery or

One of the most important nutrients for humans and plants is iron (Fe) where iron deficiency is common in nowadays human diet affecting over 2 billion people

**56**

is not known.

substances through the cuticula.

pharmaceuticals [31, 32].

**3. Nanoparticles and their action on plants**

in the world [33] Iron is essential for plant development and plays an important part in photosynthetic process being implied in redox reaction as well as generating reactive oxygen species [34]. Due to its properties iron containing nanoparticles have been used as nano-fertilizer for nutrition of plants. As an example there was observed [35] a positive effect of nano-FeO and nano-ZnCuFe oxide on the growth of mung (*Vigna radiata)* seedling, as well a positive influence on leaf and pod dry weight on soybean yield and quality [36]. The problem of high rate of accumulation of iron oxide nanoparticles in plants that conduced to precipitation in gravitational field can be solve by surface-coating materials [37], a promising way to improve the agronomic traits. Surface iron coating materials as nano-Fe2O3 coordinated with humic acid improved the mobility of iron in peanuts [38] or water-based ferrofluids stabilized with citric acid on the growth of maize [39]. In this spirit, in literature [40] there are data regarding the action of nono-iron fertilizer capped with ethylenediaminetetra acetic acid (EDTA) upon sunflower(*Helianthus annuus)* by foliar and soil application. An important parameter in studying the functional biology is plant biomass, in this regard the effect of applied nano-fertilizer by foliar treatment is the improving of aerial organ dry biomass while the effect on soil application of nano-Fe-EDTA is not conclusive. Regarding aerial organ fresh biomass both foliar and soil addition of nano-Fe-EDTA had the effect of increasing aerial organ fresh weight of the plants as compared to classic fertilizer. In this method of applying nano-Fe-EDTA there exists an increasing of leaves number in percentage by 21.42% as compared to control plants [40]. As regards, the plant height the application of nano-Fe-EDTA is effective also in foliar and soil treatment and taking into account these experiments the general growth of sunflower is influenced by iron oxide nanoparticles. The nano-fertilizer that treated the plan influenced also the physiological parameters in the sense that all treated plants had a higher chlorophyll content, the most important pigment, level than the test plants i.e. from the total level of 2.69 mg/g and 2.34 mg/g belongs to chlorophyll to the treated plants with nano-Fe-EDTA through soil absorption, indicated the translocation of coated nanoparticles from roots to the aerial parts. This treatment method implied penetration points on the leave surface i.e. stomata and subestomatic chambers which means hydrophobic penetration of nanoparticles through these pores. Another problem for foliar application of nanoparticles is the possibility for their accumulation in cells from epidermis of petiole near the application point limiting in this way their possible contribution to plant growth or photosynthesis reaction. However, the effect of an organic shell around nano-Fe made these nanoparticles more compatible for entering and translocation in the plant [40]. Another direction to suppress iron deficiency common in human diet is to use iron fertilizers based on humic substances extracted from lignites, such as leordine, it is stated [41] that this kind of fertilizer is more ecofriendly than synthetic iron chelates as discussed above, but they are less efficient in suppressing iron chlorosis. Low concentrations of superparamagnetic Fe-nanoparticles increased significantly the chlorophyll contents in sub-apical leaves of soybeans under hydroponic conditions. The plants fertilized with the leonardite humates accumulated slightly higher fresh weight than those fertilized with the iron chelate, the humic substances generally increase the shoot and root growth by 15–25% and the accumulation of total iron in pods for soybean plants reaches 50 mg/kg under conditions of sufficient nourishment [41]. The applied nanoparticles of Fe57 were capable to supply the Fe57 deficiency in plant and it was transported from root to shoot and reaches the pods, this iron humate was prepared taking into account its maximum complexing capacity in order to avoid the iron flocculation in calcareous conditions [41]. As a remark, in the context of sustainable agriculture, the Fe-nanoparticles can be considered as a part of novel technology in line with the politics of precision and sustainable agriculture.

One of the elements that results from the rapid industrialization is cadmium-Cd and as a consequence there exists an irreversible exposure in the environment, especially in the soil. The Cd absorption in the plants from soil or air through aerial deposition and its transfer into different parts of the plants can cause several abnormalities in plants as reduced growth and yield [42]. The major entry gate of Cd in plants is the roots while the toxic element entry in the human body is the consumption of contaminated food. The excess of Cd in plants affected the plant growth by reducing the production of reactive species, electrolyte leakage, hydrogen peroxide and malondialdehyde concentrations in plants [42]. As a solution to reduce the Cd content in soil is the application of biochar, as a carbon rich pyrolyzed organic biomass that is effective in reducing bioavailability of metals in soil [43]. These properties are based on biochar high pH, cation exchange capacity, nutrient retention capacity including water retention capacity and lower bulk density [44]. The use of nanotechnology in agriculture can rise different problems as the role of foliar application of ZnO nanoparticles combined with soil applied biochar in Cd accumulation by plants [45], in this regard it was stated that compared to other cereals maize (*Z. mays*) plant has a higher ability to take up Cd and its translocation to the aerial parts that conduced to Cd accumulation in grains. The effect of applied ZnO nanoparticles alone or combined with biochar enhanced the chlorophyll concentrations and gas exchange parameters in leaves of maize [45]. On the other hand, the effect upon on malondialdehyde, hydrogen peroxide, electrolyte leakage and antioxidant enzyme activities in maize leaf and roots are in the sense that the nanoparticles reduced these contents applied alone or with biochar. Experimental application of ZnO-nanoparticles improved the activities of antioxidant enzymes in leaves and roots [45]. As it was presented [45] the application of ZnO nanoparticles and biochar reduced the Cd concentration in maize shoots and roots. Generally the revealing that ZnO nanoparticles with effect in maize biomass and growth is expressed by accelerated exogenous application of nanoparticles further enhanced with biochar application in combination to nanoparticles. It was observed [45] that the lower biomass in control plants is associated with higher Cd concentration in maize which reduced the chlorophyll concentration in leaves, or due to the increased levels of malondialdehyde, hydrogen peroxide and electrolyte leakage in the belowground and aboveground tissues. Lower concentration of ZnO nanoparticles have positive impacts on plants [46] in the sense that the height of the plants increased and the biochar application decreased the soluble Cd in soil, meanwhile nanoparticles increased the Zn level in the plants [45]. Exogenous application of ZnO nanoparticles improved the chlorophyll concentration and as a consequence improved photosynthesis and with applied amendments might reduce the oxidative stress in maize plants. It was suggested [47] that ZnO nanoparticles can be considered as slow-release for Zn fertilizers which is advantageous to avoid sudden absorption of Zn by plants as the higher concentrations of Zn absorbed by the plants also conduced to toxicity in plants. It was stated [48] that a proper amount of Zn in the soil or plants may interfere with Cd and could reduce the Cd accumulation by plants due to the antagonistic effects of these metals on each other and furthermore biochar application in combination with ZnO nanoparticles further deceased Cd concentration in maize plants. As a solution to Zn malnutrition, the strategy of using ZnO nanoparticles combined with biochar in cereals growth, in particular in maize, conduced to the enhancement in plant biomass with decreased Cd concentration in cereals. A proper concentration of Zn is benefic to plant organism because Zn is necessary for the activity of enzymes such as dehydrogenases, aldolases, isomerases, transphosphorylases and RNA and DNA polymerases, as well as in synthesis of tryptophan, cell division, maintenance of membrane structure and photosynthesis and acts as a regulatory cofactor in protein synthesis [49].

**59**

mon or peach.

*Application of Nanotechnology Solutions in Plants Fertilization*

For example in coffee plants although Zn is required for optimal metabolism, yet deficiency is prevalent partly due to the inefficient absorption of this micronutrient combined with a deficiency in translocation [50]. Zn fertilization improves the production and quality of coffee beans by positive impact on polyphenol oxidase activity, color index, sucrose content, caffeine and trigonelline content and chlorogenic acid [49]. One of the most efficient ways of suppressing Zn deficiency is foliar fertilization a method that avoids toxicity symptoms and reduce fertilizer-related pollution and in this perspective the foliar fertilization using micronutrients as Zn nanoparticles is the advanced solution proposed by nanotechnology. In spite of positive physiological impacts of nanoparticle fertilizers on crop growth, the properties of nanoparticles can induce oxidative stress and toxicity in plants and other organisms in ecosystem [51]. It was observed [52] the effect of ZnO nanoparticles application on coffee plant on its positive part, i.e. the fresh weight of roots and leaves are increased in percentages of 37% (root) and 95% (leaves) and no effect on the stem as compared to control. The net photosynthesis rate did not vary over time for ZnO nanoparticles treated plants and as regards zinc assimilation ZnO nanoparticles treated leaves contained a higher content of Zn compared to classical nutrient ZnSO4 treated plants [52]. As regards, the zinc assimilation in stems and roots there does not exist significant differences between the treated plants with ZnO nanoparticles and zinc sulfate at the same content of Zn in the soil. The treatment of coffee plants with ZnO nanoparticles positively affected plant biomass, with a major effect on fresh and dry weight. Part of so-called photosynthetic machinery was improved when coffee plants were exposed to ZnO nanoparticles, there exists a positive interaction between ZnO nanoparticles and net carbon assimilation rate and stomatal conductance, confirming the role of Zn as a cofactor of carbonic anhydrase that increases the content of CO2 in the chloroplast and thus also increases the carboxylation capability of the Rubisco enzyme [53]. It is important to state that although Zn is an essential element, in an impropriate quantity it can reduce plant health and performance at phytotoxic concentrations. Symptoms of Zn toxicity are reduced growth and plant biomass, inhibition of cell elongation and division, wilting, curling and rolling of young leaves chlorotic and necrotic leaf

The effect of nano-boron (B) fertilizer on the mineral nutrition and fruit yield was put into evidence by on pomegranate trees culture [55]. It was observed that a

increased significantly the fruit yield up to 34% depending on treatment, with an accent to nano-B fertilizer. Also, the foliar application of these nano-fertilizers increased the number of fruits per tree, without an effect upon fruit cracking. As regards the fruit size physical parameters as fruit diameter, fruit calvyx diameter or average weight, they are not affected significantly for the treated trees, but the pH pomegranate juice increased to 0.62 pH units under fertilization. Concentrated nano-B foliar application caused small (1%) but statistically constant changes in the amount of total phenolic compounds in pomegranate juice whereas the antioxidant activity is not affected. The total amount of sugar in pomegranate fruit juice increased up to 4.6% at discussed nano-B concentration with no significantly increase in total anthocyanins under treatment. The action of nano-B fertilizers is also efficient in fruit crops as almond, apple, pear, persim-

Calcium (Ca) is an important macro-element that plays an important role in plants including structural functions of cell walls, stabilization of cell membrane, maintenance of cell turgor pressure and counter-ion for inorganic and organic anions in vacuoles, as well as cytoplasmic messenger. Calcium cannot be transferred through from the older tissue to other parts of plant on the basic phloem pathway

) in combination with nano-Zn

*DOI: http://dx.doi.org/10.5772/intechopen.91240*

tips and root growth inhibition [54].

foliar spray of nano-B (concentration 6.5 mg BL<sup>−</sup><sup>1</sup>

### *Application of Nanotechnology Solutions in Plants Fertilization DOI: http://dx.doi.org/10.5772/intechopen.91240*

*Urban Horticulture - Necessity of the Future*

One of the elements that results from the rapid industrialization is cadmium-Cd and as a consequence there exists an irreversible exposure in the environment, especially in the soil. The Cd absorption in the plants from soil or air through aerial deposition and its transfer into different parts of the plants can cause several abnormalities in plants as reduced growth and yield [42]. The major entry gate of Cd in plants is the roots while the toxic element entry in the human body is the consumption of contaminated food. The excess of Cd in plants affected the plant growth by reducing the production of reactive species, electrolyte leakage, hydrogen peroxide and malondialdehyde concentrations in plants [42]. As a solution to reduce the Cd content in soil is the application of biochar, as a carbon rich pyrolyzed organic biomass that is effective in reducing bioavailability of metals in soil [43]. These properties are based on biochar high pH, cation exchange capacity, nutrient retention capacity including water retention capacity and lower bulk density [44]. The use of nanotechnology in agriculture can rise different problems as the role of foliar application of ZnO nanoparticles combined with soil applied biochar in Cd accumulation by plants [45], in this regard it was stated that compared to other cereals maize (*Z. mays*) plant has a higher ability to take up Cd and its translocation to the aerial parts that conduced to Cd accumulation in grains. The effect of applied ZnO nanoparticles alone or combined with biochar enhanced the chlorophyll concentrations and gas exchange parameters in leaves of maize [45]. On the other hand, the effect upon on malondialdehyde, hydrogen peroxide, electrolyte leakage and antioxidant enzyme activities in maize leaf and roots are in the sense that the nanoparticles reduced these contents applied alone or with biochar. Experimental application of ZnO-nanoparticles improved the activities of antioxidant enzymes in leaves and roots [45]. As it was presented [45] the application of ZnO nanoparticles and biochar reduced the Cd concentration in maize shoots and roots. Generally the revealing that ZnO nanoparticles with effect in maize biomass and growth is expressed by accelerated exogenous application of nanoparticles further enhanced with biochar application in combination to nanoparticles. It was observed [45] that the lower biomass in control plants is associated with higher Cd concentration in maize which reduced the chlorophyll concentration in leaves, or due to the increased levels of malondialdehyde, hydrogen peroxide and electrolyte leakage in the belowground and aboveground tissues. Lower concentration of ZnO nanoparticles have positive impacts on plants [46] in the sense that the height of the plants increased and the biochar application decreased the soluble Cd in soil, meanwhile nanoparticles increased the Zn level in the plants [45]. Exogenous application of ZnO nanoparticles improved the chlorophyll concentration and as a consequence improved photosynthesis and with applied amendments might reduce the oxidative stress in maize plants. It was suggested [47] that ZnO nanoparticles can be considered as slow-release for Zn fertilizers which is advantageous to avoid sudden absorption of Zn by plants as the higher concentrations of Zn absorbed by the plants also conduced to toxicity in plants. It was stated [48] that a proper amount of Zn in the soil or plants may interfere with Cd and could reduce the Cd accumulation by plants due to the antagonistic effects of these metals on each other and furthermore biochar application in combination with ZnO nanoparticles further deceased Cd concentration in maize plants. As a solution to Zn malnutrition, the strategy of using ZnO nanoparticles combined with biochar in cereals growth, in particular in maize, conduced to the enhancement in plant biomass with decreased Cd concentration in cereals. A proper concentration of Zn is benefic to plant organism because Zn is necessary for the activity of enzymes such as dehydrogenases, aldolases, isomerases, transphosphorylases and RNA and DNA polymerases, as well as in synthesis of tryptophan, cell division, maintenance of membrane structure and photosynthesis and acts as a regulatory cofactor in protein synthesis [49].

**58**

For example in coffee plants although Zn is required for optimal metabolism, yet deficiency is prevalent partly due to the inefficient absorption of this micronutrient combined with a deficiency in translocation [50]. Zn fertilization improves the production and quality of coffee beans by positive impact on polyphenol oxidase activity, color index, sucrose content, caffeine and trigonelline content and chlorogenic acid [49]. One of the most efficient ways of suppressing Zn deficiency is foliar fertilization a method that avoids toxicity symptoms and reduce fertilizer-related pollution and in this perspective the foliar fertilization using micronutrients as Zn nanoparticles is the advanced solution proposed by nanotechnology. In spite of positive physiological impacts of nanoparticle fertilizers on crop growth, the properties of nanoparticles can induce oxidative stress and toxicity in plants and other organisms in ecosystem [51]. It was observed [52] the effect of ZnO nanoparticles application on coffee plant on its positive part, i.e. the fresh weight of roots and leaves are increased in percentages of 37% (root) and 95% (leaves) and no effect on the stem as compared to control. The net photosynthesis rate did not vary over time for ZnO nanoparticles treated plants and as regards zinc assimilation ZnO nanoparticles treated leaves contained a higher content of Zn compared to classical nutrient ZnSO4 treated plants [52]. As regards, the zinc assimilation in stems and roots there does not exist significant differences between the treated plants with ZnO nanoparticles and zinc sulfate at the same content of Zn in the soil. The treatment of coffee plants with ZnO nanoparticles positively affected plant biomass, with a major effect on fresh and dry weight. Part of so-called photosynthetic machinery was improved when coffee plants were exposed to ZnO nanoparticles, there exists a positive interaction between ZnO nanoparticles and net carbon assimilation rate and stomatal conductance, confirming the role of Zn as a cofactor of carbonic anhydrase that increases the content of CO2 in the chloroplast and thus also increases the carboxylation capability of the Rubisco enzyme [53]. It is important to state that although Zn is an essential element, in an impropriate quantity it can reduce plant health and performance at phytotoxic concentrations. Symptoms of Zn toxicity are reduced growth and plant biomass, inhibition of cell elongation and division, wilting, curling and rolling of young leaves chlorotic and necrotic leaf tips and root growth inhibition [54].

The effect of nano-boron (B) fertilizer on the mineral nutrition and fruit yield was put into evidence by on pomegranate trees culture [55]. It was observed that a foliar spray of nano-B (concentration 6.5 mg BL<sup>−</sup><sup>1</sup> ) in combination with nano-Zn increased significantly the fruit yield up to 34% depending on treatment, with an accent to nano-B fertilizer. Also, the foliar application of these nano-fertilizers increased the number of fruits per tree, without an effect upon fruit cracking. As regards the fruit size physical parameters as fruit diameter, fruit calvyx diameter or average weight, they are not affected significantly for the treated trees, but the pH pomegranate juice increased to 0.62 pH units under fertilization. Concentrated nano-B foliar application caused small (1%) but statistically constant changes in the amount of total phenolic compounds in pomegranate juice whereas the antioxidant activity is not affected. The total amount of sugar in pomegranate fruit juice increased up to 4.6% at discussed nano-B concentration with no significantly increase in total anthocyanins under treatment. The action of nano-B fertilizers is also efficient in fruit crops as almond, apple, pear, persimmon or peach.

Calcium (Ca) is an important macro-element that plays an important role in plants including structural functions of cell walls, stabilization of cell membrane, maintenance of cell turgor pressure and counter-ion for inorganic and organic anions in vacuoles, as well as cytoplasmic messenger. Calcium cannot be transferred through from the older tissue to other parts of plant on the basic phloem pathway

and Ca xylem translocation depends on unidirectional transpiration stream [56]. Studies of foliar application of nano-Ca on pomegranate trees shows no significant effect on fruit yield and to the number of fruits per trees [57]. Nano-Ca fertilization increased the Ca leaf concentration, whereas the foliar treatment decreased significantly pomegranate fruit cracking. The total phenolic compounds in pomegranate fruit juice is decreased in nano-Ca fertilization but with no significant effect on antioxidant activity and total anthocyanin content. Foliar application of Ca reduces the fruit cracking due to its role on cell wall, in enhancing the mechanical properties of plant tissue. However, the foliar fertilization of Ca had no significant effect on yields for kiwifruit, strawberry, grape and cherry.

Manganese (Mn) is a micronutrient required by most of the plants die to its implication in biochemical reactions, as those required by dehydrogenases, decarboxylases, kinases, oxidases, peroxidases enzymes and to their role in fighting oxygen reactive species in plants. Plants required 20–40 mg Mn/kg of dry weight for its various functions e.g. in tricarboxylic acid cycle, oxidative and non-oxidative decarboxylation reactions and for different synthesis as carotenoids, sterols or gibberellic acid. The most important process of photosynthesis, implied the final conversion of absorbed light to energy via enzymatic reactions. Among them, a studied Mn-containing enzyme, is found in PSII oxygen evolving complex, a multi-step enzymatic pathway where Mn is required, as a cofactor in both lower and higher plants for the Hill reaction-the water splitting and oxygen evolving system [58]. Mn plays an important role in the synthesis of fatty acids and carotenoids, as well as in cell division and elongation. A normal function of the plant as biological system is affected by abiotic stress defined any adverse force or condition that affects its normal functioning. Abiotic stresses as drought, flood, salinity or harsh temperature conduced to an excessive amounts of reactive oxygen species that potentially injure proteins, membrane lipids, carbohydrates and DNA. The application of Mn increased the leaf area, photosynthesis rate and stomatal conductance in drought stress conditions, reducing the production of reactive oxygen species in plants. These reactive species also accumulated in inside the plants under thermal stress as harsh temperatures, that causes damage to cellular compounds and metabolic processes. It was suggested [59] that salinity inhibits the uptake of Mn inside plants inducing deficiency, in this case the foliar application increased stem diameter, fresh and dry biomass, number of seeds and different biochemical parameters as total protein or Hill reaction activity. The application of Mn nanoparticles on wheat applied by foliar exposure or soil amendment showed [60] no inhibition of vegetative or reproductive development, further more Mn nanoparticles significantly reduced Mn accumulation in shoots but increased the translocation efficiency in grains compared to classical Mn fertilizers due to a greater reactivity and non-toxicity due to a slower and a continuously availability of soluble Mn from Mn nanoparticles as compared to ionic Mn salt. The Mn nanoparticles greater photophosphorylation and oxygen evolution compared to bulk Mn suggested its novel potential nano modulator of the photochemical pathway in agriculture [61]. Furthermore Mn nanoparticles are viewed as a stimulant of plant growth and of metabolic processes as alkaloids production. In infested soils, foliar exposure to Mn oxide nanoparticles reduces disease up to 28% as compared to controls [62], the plants can have cross-tolerance between abiotic and biotic stresses, and in this regard stress tolerance can help plants to form faster and more resistant manner to additional environmental changes. The propose mechanism for the distribution of Mn nanoparticles through the plant incudes transportation from the root through the vascular system, a process considered as active-transporting as long as includes signaling, recycling and plasma membrane regulation. Generally the excess amounts of Mn in plants is not benefic to their health by interfering with the

**61**

*Application of Nanotechnology Solutions in Plants Fertilization*

proper plant growth is in the range of only 0.02 mg L<sup>−</sup><sup>1</sup>

Copper nanoparticles at low concentrations (<0.25 mg L<sup>−</sup><sup>1</sup>

uptake, transport and utilization of other minerals as Ca, Fe or Mg as being com-

photosynthesis in a percentage of 35% on waterweed (*Elodea. densa planch*) compared with control plants [63]. It was stated [64] that soil amendments with

tuce seedling growth up to 91% without toxic effects. Higher concentrations up

growth of mung bean and wheat [65] and can reduce the biomass of zucchini by 90% as compared to control. The optimal concentration for aqueous copper for

with regular application of Fe and Mg [67]. The Mg nanoparticles application improved the uptake of Mg in plant stems and leaves compared to the use of regular Mg salts, a fact related to the higher mobility of Mg nanoparticles. Magnesium deficiency conduced to a slow growth of plant and to leaves problems due to the development of internal chlorosis and that is why Mg important in crop yield. Silver (Ag) is known as an element with antiseptic characteristics and it is important to understand its effect upon soil microbial community. Microorganisms are key regulators of biogeochemical recycling of nutrients in the environment and assist in maintaining the overall health and function of ecosystems [68]. The soil is regarded as a complex system and its physicochemical characteristics as pH, texture and organic matter content can influence the nanoparticles properties introduced in it, a fact that can conduce to an increased or a decreased bioavailability and toxicity of nanoparticles. The effect of Ag nanoparticles on the microbial diversity and enzyme activity of soil is regarded as a significant decrease in microbial mass as a function of increasing Ag nanoparticles concentration. [69]. Ag nanoparticles had impact on vascular plants, presenting positive or negative effects on seed germination, root growth and plant biomass [70]. In Ag nanoparticles application on wheat plants, there was not observed a significant effect with the exception of root fresh weight and root length that presents a negative response at 75 ppm treatment while in cowpea and *Brassica* there was observed a positive response to Ag nanoparticles. In cowpea plants a 50 ppm concentration of Ag nanoparticles conduced to growth promotion and increased root nodulation suggesting that Ag nanoparticles treatment improved the growth by modulating the antioxidant action of nanoparticles. Increased nodulation is supposed to be related to nitrogen-fixing bacteria as long as root exudation pattern is dependent to Ag nanoparticles concentration. In soil, total bacteria count improved in 50 ppm treatment and nitrogen fixer bacteria are sensitive toward 75 ppm treatment. In cowpea, the total bacteria count declined with increasing Ag nanoparticles concentration, with an increase of diversity index of total bacteria population was observed in 50 ppm treatment whereas the diversity of nitrogen fixers decreased in the 75 ppm treatment. The impact of Ag nanoparticles on soil bacteria diversity is dependent on Ag nanoparticles concentration and on the other hand on the plant species grown in that soil, a specificity related to the different root exudation patterns of different plant species. The antimicrobial properties of Ag nanoparticles may be altered when released in soil due to the

Magnesium (Mg) is essential for plant growth as it plays an important role in the photosynthesis process as central component of chlorophyll and also acts as a phosphorus carrier as an important element for phosphate metabolism. Mg is necessary in cell division and protein formation in activation of several enzyme systems and is essential for plant respiration. The effect of foliar application of magnesium and iron nanoparticles solutions upon black-eyed pea (*Vigna unguiculata*) combined in

of metallic Cu nanoparticles conduced to toxic effects on seedling

enhanced the 1000-seed weight by 7% in comparison

) stimulated plant

due to the effect of phytox-

increased significantly 15-day let-

*DOI: http://dx.doi.org/10.5772/intechopen.91240*

metallic Cu nanoparticles up to 600 mg kg<sup>−</sup><sup>1</sup>

petitive for the same ion transport.

to 1000 mg L<sup>−</sup><sup>1</sup>

icity at higher levels [66].

a concentration of 0.5 g L<sup>−</sup><sup>1</sup>

*Urban Horticulture - Necessity of the Future*

yields for kiwifruit, strawberry, grape and cherry.

and Ca xylem translocation depends on unidirectional transpiration stream [56]. Studies of foliar application of nano-Ca on pomegranate trees shows no significant effect on fruit yield and to the number of fruits per trees [57]. Nano-Ca fertilization increased the Ca leaf concentration, whereas the foliar treatment decreased significantly pomegranate fruit cracking. The total phenolic compounds in pomegranate fruit juice is decreased in nano-Ca fertilization but with no significant effect on antioxidant activity and total anthocyanin content. Foliar application of Ca reduces the fruit cracking due to its role on cell wall, in enhancing the mechanical properties of plant tissue. However, the foliar fertilization of Ca had no significant effect on

Manganese (Mn) is a micronutrient required by most of the plants die to its implication in biochemical reactions, as those required by dehydrogenases, decarboxylases, kinases, oxidases, peroxidases enzymes and to their role in fighting oxygen reactive species in plants. Plants required 20–40 mg Mn/kg of dry weight for its various functions e.g. in tricarboxylic acid cycle, oxidative and non-oxidative decarboxylation reactions and for different synthesis as carotenoids, sterols or gibberellic acid. The most important process of photosynthesis, implied the final conversion of absorbed light to energy via enzymatic reactions. Among them, a studied Mn-containing enzyme, is found in PSII oxygen evolving complex, a multi-step enzymatic pathway where Mn is required, as a cofactor in both lower and higher plants for the Hill reaction-the water splitting and oxygen evolving system [58]. Mn plays an important role in the synthesis of fatty acids and carotenoids, as well as in cell division and elongation. A normal function of the plant as biological system is affected by abiotic stress defined any adverse force or condition that affects its normal functioning. Abiotic stresses as drought, flood, salinity or harsh temperature conduced to an excessive amounts of reactive oxygen species that potentially injure proteins, membrane lipids, carbohydrates and DNA. The application of Mn increased the leaf area, photosynthesis rate and stomatal conductance in drought stress conditions, reducing the production of reactive oxygen species in plants. These reactive species also accumulated in inside the plants under thermal stress as harsh temperatures, that causes damage to cellular compounds and metabolic processes. It was suggested [59] that salinity inhibits the uptake of Mn inside plants inducing deficiency, in this case the foliar application increased stem diameter, fresh and dry biomass, number of seeds and different biochemical parameters as total protein or Hill reaction activity. The application of Mn nanoparticles on wheat applied by foliar exposure or soil amendment showed [60] no inhibition of vegetative or reproductive development, further more Mn nanoparticles significantly reduced Mn accumulation in shoots but increased the translocation efficiency in grains compared to classical Mn fertilizers due to a greater reactivity and non-toxicity due to a slower and a continuously availability of soluble Mn from Mn nanoparticles as compared to ionic Mn salt. The Mn nanoparticles greater photophosphorylation and oxygen evolution compared to bulk Mn suggested its novel potential nano modulator of the photochemical pathway in agriculture [61]. Furthermore Mn nanoparticles are viewed as a stimulant of plant growth and of metabolic processes as alkaloids production. In infested soils, foliar exposure to Mn oxide nanoparticles reduces disease up to 28% as compared to controls [62], the plants can have cross-tolerance between abiotic and biotic stresses, and in this regard stress tolerance can help plants to form faster and more resistant manner to additional environmental changes. The propose mechanism for the distribution of Mn nanoparticles through the plant incudes transportation from the root through the vascular system, a process considered as active-transporting as long as includes signaling, recycling and plasma membrane regulation. Generally the excess amounts of Mn in plants is not benefic to their health by interfering with the

**60**

uptake, transport and utilization of other minerals as Ca, Fe or Mg as being competitive for the same ion transport.

Copper nanoparticles at low concentrations (<0.25 mg L<sup>−</sup><sup>1</sup> ) stimulated plant photosynthesis in a percentage of 35% on waterweed (*Elodea. densa planch*) compared with control plants [63]. It was stated [64] that soil amendments with metallic Cu nanoparticles up to 600 mg kg<sup>−</sup><sup>1</sup> increased significantly 15-day lettuce seedling growth up to 91% without toxic effects. Higher concentrations up to 1000 mg L<sup>−</sup><sup>1</sup> of metallic Cu nanoparticles conduced to toxic effects on seedling growth of mung bean and wheat [65] and can reduce the biomass of zucchini by 90% as compared to control. The optimal concentration for aqueous copper for proper plant growth is in the range of only 0.02 mg L<sup>−</sup><sup>1</sup> due to the effect of phytoxicity at higher levels [66].

Magnesium (Mg) is essential for plant growth as it plays an important role in the photosynthesis process as central component of chlorophyll and also acts as a phosphorus carrier as an important element for phosphate metabolism. Mg is necessary in cell division and protein formation in activation of several enzyme systems and is essential for plant respiration. The effect of foliar application of magnesium and iron nanoparticles solutions upon black-eyed pea (*Vigna unguiculata*) combined in a concentration of 0.5 g L<sup>−</sup><sup>1</sup> enhanced the 1000-seed weight by 7% in comparison with regular application of Fe and Mg [67]. The Mg nanoparticles application improved the uptake of Mg in plant stems and leaves compared to the use of regular Mg salts, a fact related to the higher mobility of Mg nanoparticles. Magnesium deficiency conduced to a slow growth of plant and to leaves problems due to the development of internal chlorosis and that is why Mg important in crop yield.

Silver (Ag) is known as an element with antiseptic characteristics and it is important to understand its effect upon soil microbial community. Microorganisms are key regulators of biogeochemical recycling of nutrients in the environment and assist in maintaining the overall health and function of ecosystems [68]. The soil is regarded as a complex system and its physicochemical characteristics as pH, texture and organic matter content can influence the nanoparticles properties introduced in it, a fact that can conduce to an increased or a decreased bioavailability and toxicity of nanoparticles. The effect of Ag nanoparticles on the microbial diversity and enzyme activity of soil is regarded as a significant decrease in microbial mass as a function of increasing Ag nanoparticles concentration. [69]. Ag nanoparticles had impact on vascular plants, presenting positive or negative effects on seed germination, root growth and plant biomass [70]. In Ag nanoparticles application on wheat plants, there was not observed a significant effect with the exception of root fresh weight and root length that presents a negative response at 75 ppm treatment while in cowpea and *Brassica* there was observed a positive response to Ag nanoparticles. In cowpea plants a 50 ppm concentration of Ag nanoparticles conduced to growth promotion and increased root nodulation suggesting that Ag nanoparticles treatment improved the growth by modulating the antioxidant action of nanoparticles. Increased nodulation is supposed to be related to nitrogen-fixing bacteria as long as root exudation pattern is dependent to Ag nanoparticles concentration. In soil, total bacteria count improved in 50 ppm treatment and nitrogen fixer bacteria are sensitive toward 75 ppm treatment. In cowpea, the total bacteria count declined with increasing Ag nanoparticles concentration, with an increase of diversity index of total bacteria population was observed in 50 ppm treatment whereas the diversity of nitrogen fixers decreased in the 75 ppm treatment. The impact of Ag nanoparticles on soil bacteria diversity is dependent on Ag nanoparticles concentration and on the other hand on the plant species grown in that soil, a specificity related to the different root exudation patterns of different plant species. The antimicrobial properties of Ag nanoparticles may be altered when released in soil due to the

complex system of biotic and abiotic processes, e.g. pore-water harbors a range of electrolytes that increase the aggregation of Ag nanoparticles in soil, thus reducing its size-dependent toxicity. The plants cultured in artificial soils compared to agar conditions in addition to higher concentration of Ag<sup>+</sup> ions the plants exhibited some characteristics: (a) the apparent toxicity observed in the soil was attributable to the particle toxicity; (b) lower rates of nanoparticles dissolution can be attributed to the reduction in the surface and greater soil aggregation; (c) the agar and soil have different mechanisms for sorption of the dissolved Ag<sup>+</sup> ion and the Ag nanoparticles. The application of Ag nanoparticles in real soil improved the bactericidal and fungicidal effectiveness of silver against most important plant pathogenic fungi.

Titanium oxide (TiO2) mineral is naturally occurred in four natural polymorphs: akaogiite (monoclinic), brookite (orthorhombic), anatase (tetragonal) and rutile (tetragonal). TiO2 nanoparticles are explored due their use as an antimicrobial agent and photocatalyst in order to remove organic compounds from contaminated air, soil, and water. Ti is not an essential element for plants, therefore TiO2 nanoparticles are not viewed as plant nutrients but plays a potential role in plant protection and at lower doses its effective to its properties as a photocatalysts or an UV protector. It was stated [71] that exposure of naturally aged spinach seeds to TiO2 nanoparticles (rutile) at concentration of 250–4000 mg L<sup>−</sup><sup>1</sup> significantly increased the germination rate, the germination index, the dry weight of seedlings and vigor index of seeds. It was observed that under hydroponic conditions on agar, TiO2 nanoparticles generally cause positive or non-consequential effects on plant growth for different food crops. For example, in hydroponic conditions it was observed a significant increase in the root and shoot length of *Brassica juncea* seedling treated with TiO2 nanoparticles at concentrations: (0, 200, 500, 1000 and 1500 mg L<sup>−</sup><sup>1</sup> ). An important factor is the lack of toxicity of TiO2 nanoparticles due to their rapid agglomeration and consequently formation of larger hydrodynamic particles that are not available to plant and have no effect on plants, this is a property of rutile form that presented the characteristic of lipophilicity. It was observed [72] that TiO2 in anatase form are toxic at high concentrations and due to their antimicrobial properties a significant growth of the roots was observed.

Selenium (Se) is an essential trace element for humans and animals and is beneficial for plants at low concentrations particularly under stress conditions acting like an antioxidant. Cereals are a good source of Se as it is present in the form of Se-methionine [73]. The total concentration of Se in most of soils is 0.1–2 mg kg<sup>−</sup><sup>1</sup> , with factors that affects Se solubility as: soil pH, redox potential, calcium carbonate level, cation exchange capacity, organic carbon, iron and aluminum level as well as the plants capability to produce root exudates. Selenium is most available in alkaline soils in the form of selenite, in acidic poorly aerated Se occurs in insoluble selenide forms, the lower limit for Se concentration in soil is 0.5 mg kg<sup>−</sup><sup>1</sup> . Selenium fertilization rate and its chemical form directly influenced Se grain concentration affecting the yield, its application form being foliar or liquid on the soil surface. Low concentrations of Se had a positive effect on growth of ryegrass, lettuce and potato due to its antioxidant action. It was stated [74] that 10 g Se selenite per ha can increase wheat Se concentration from a base level of 30–100-200 μg kg<sup>−</sup><sup>1</sup> to recommended level of 300 μg kg<sup>−</sup><sup>1</sup> as a minimum target. Agronomic use efficiency is higher for foliar application than soil application. Agronomic bio-fortification is an inexpensive method for the increase of Se intake by humans but the limited Se resources indicated that fertilization strategies had to increase agronomic use efficiency in environmental conditions by improving agro-technical measures.

Silicon dioxide (SiO2) is a form of silicon oxide that had abundance in environmental mostly in the soil. Lower amounts of nano-SiO2 increased germination of seeds in tomato [75], or of *Lycopersicum esculentum* seeds germination in

**63**

*Application of Nanotechnology Solutions in Plants Fertilization*

rate electron transport and photochemical quell [79].

nano-SiO2 for a percentage of 22.16%. The same concentra-

tion increased the fresh weight of seedlings by 116.58% and seedlings dry weight by 117.46% compared to control, with an important action upon root and shoot growth. Nano-SiO2 amplified various factors of the growth and conditions of seedlings, i.e. height, diameter of root collar, main length of roots, seedlings lateral root number as well as induction of chlorophyll synthesis. Under abiotic stress nano-SiO2 increases seeds germination in tomato [76] and in saline conditions nano-SiO2 maximized the fresh and dry weight of leaves confirmed that the increment in the proline accumulation, unattached amino-acids, nutrient quantity and antioxidant activity of enzymes increased plant's level of endurance to environmental stress [77]. The chlorophyll content developed on nano-SiO2 treated plants grown in salt-stressed conditions, the application of 1 mM silicon dioxide could alleviate the side effect of salt stress on percentage of germination, length, of root and shoot, weight of seedling, mean germination rate see vigor index and cotyledon reserve mobilization of *Lens culinaris* [78]. Nano silicon dioxide developed the growth of the plant, net rate photosynthesis, level of transpiration, conductance of stomata,

Regarding the nanotoxicity of nanoparticles action, the involved mechanism is not entirely understand, this mechanism is assumed in the sense by the changes related to the chemical structure, particles size and active surface area of nanoparticles. It is stated [80] that the toxicity action is focused on two directions: i.e. (a) a chemical toxicity based on the chemical composition as the released of toxic ions and (b) stress or stimuli caused by the surface, size or shape of particles. As viewed from chemical physics processes, the solubility of oxide nanoparticles affects the cell culture response and nanoparticle mediated toxicity is partly explained by the release of dissolved components of them [81]. In comparison to metal toxicity in plants and animals, the nanoparticles pathway is different, a problem solved by the introduction of different parameters in experimental tests to evaluate the nanoparticles dynamics. In a plant culture exposed to nanoparticles, the gain and losses related to the development, growth and productivity are not exclusively part of nanoparticles effect but they can be viewed as a participation of the primary ions to biological processes active in plants. Regarding the presence of nanoparticles in soil, as culture area for plants, had to be considered the interaction with the microorganisms in soil because they can positively interact with plants e.g. arbuscular mycorrhizal fungi [80]. The nanoparticles interaction with plants e.g. accumulation in plant biomass affects their fate and transport in the environment. There exists a first report [82] in 2007 regarding the negative effects of nanoparticles upon several plants as corn, cucumber, soybean, cabbage and carrot at relatively low dosage. At microscopic scale, the analysis of the chromosome morphology showed a relation between increased number of aberrations and the increased concentration of nanoparticles e.g. the appearance of stick chromosomes [83]. The phyto-toxicity was observed at molecular and nuclear cell level because the occurrence of stick chromosomes might be related to the degradation or de-polymerization of chromosomal DNA [80]. The extended development of modern agriculture brings besides some true benefits regarding crop productivity increasing problems related to environmental contamination with toxic elements e.g. metals or pesticides compounds and from this point of view nanoparticles used can aggravate the situation. The process of heavy metals accumulation by plants is related for the large majority of plants to roots accumulation and only a small part is translocated to the aboveground of the plants [84]. There are evidence [85] to a translocation process from the roots to the fruits, without the existence of changes due to biochemical processes. It is important to note that the concentration, plant organ or tissue, exposure rate, elemental form, plant species, exposure dosage (chronic/acute) affects the plant

*DOI: http://dx.doi.org/10.5772/intechopen.91240*

concentration of 8 g L<sup>−</sup><sup>1</sup>

### *Application of Nanotechnology Solutions in Plants Fertilization DOI: http://dx.doi.org/10.5772/intechopen.91240*

*Urban Horticulture - Necessity of the Future*

conditions in addition to higher concentration of Ag<sup>+</sup>

different mechanisms for sorption of the dissolved Ag<sup>+</sup>

nanoparticles (rutile) at concentration of 250–4000 mg L<sup>−</sup><sup>1</sup>

properties a significant growth of the roots was observed.

forms, the lower limit for Se concentration in soil is 0.5 mg kg<sup>−</sup><sup>1</sup>

wheat Se concentration from a base level of 30–100-200 μg kg<sup>−</sup><sup>1</sup>

environmental conditions by improving agro-technical measures.

complex system of biotic and abiotic processes, e.g. pore-water harbors a range of electrolytes that increase the aggregation of Ag nanoparticles in soil, thus reducing its size-dependent toxicity. The plants cultured in artificial soils compared to agar

characteristics: (a) the apparent toxicity observed in the soil was attributable to the particle toxicity; (b) lower rates of nanoparticles dissolution can be attributed to the reduction in the surface and greater soil aggregation; (c) the agar and soil have

ticles. The application of Ag nanoparticles in real soil improved the bactericidal and fungicidal effectiveness of silver against most important plant pathogenic fungi.

the germination rate, the germination index, the dry weight of seedlings and vigor index of seeds. It was observed that under hydroponic conditions on agar, TiO2 nanoparticles generally cause positive or non-consequential effects on plant growth for different food crops. For example, in hydroponic conditions it was observed a significant increase in the root and shoot length of *Brassica juncea* seedling treated with TiO2 nanoparticles at concentrations: (0, 200, 500, 1000 and 1500 mg L<sup>−</sup><sup>1</sup>

An important factor is the lack of toxicity of TiO2 nanoparticles due to their rapid agglomeration and consequently formation of larger hydrodynamic particles that are not available to plant and have no effect on plants, this is a property of rutile form that presented the characteristic of lipophilicity. It was observed [72] that TiO2 in anatase form are toxic at high concentrations and due to their antimicrobial

Selenium (Se) is an essential trace element for humans and animals and is beneficial for plants at low concentrations particularly under stress conditions acting like an antioxidant. Cereals are a good source of Se as it is present in the form of Se-methionine [73]. The total concentration of Se in most of soils is 0.1–2 mg kg<sup>−</sup><sup>1</sup>

with factors that affects Se solubility as: soil pH, redox potential, calcium carbonate level, cation exchange capacity, organic carbon, iron and aluminum level as well as the plants capability to produce root exudates. Selenium is most available in alkaline soils in the form of selenite, in acidic poorly aerated Se occurs in insoluble selenide

tion rate and its chemical form directly influenced Se grain concentration affecting the yield, its application form being foliar or liquid on the soil surface. Low concentrations of Se had a positive effect on growth of ryegrass, lettuce and potato due to its antioxidant action. It was stated [74] that 10 g Se selenite per ha can increase

foliar application than soil application. Agronomic bio-fortification is an inexpensive method for the increase of Se intake by humans but the limited Se resources indicated that fertilization strategies had to increase agronomic use efficiency in

Silicon dioxide (SiO2) is a form of silicon oxide that had abundance in environmental mostly in the soil. Lower amounts of nano-SiO2 increased germination of seeds in tomato [75], or of *Lycopersicum esculentum* seeds germination in

as a minimum target. Agronomic use efficiency is higher for

Titanium oxide (TiO2) mineral is naturally occurred in four natural polymorphs: akaogiite (monoclinic), brookite (orthorhombic), anatase (tetragonal) and rutile (tetragonal). TiO2 nanoparticles are explored due their use as an antimicrobial agent and photocatalyst in order to remove organic compounds from contaminated air, soil, and water. Ti is not an essential element for plants, therefore TiO2 nanoparticles are not viewed as plant nutrients but plays a potential role in plant protection and at lower doses its effective to its properties as a photocatalysts or an UV protector. It was stated [71] that exposure of naturally aged spinach seeds to TiO2

ions the plants exhibited some

ion and the Ag nanopar-

significantly increased

).

,

. Selenium fertiliza-

to recommended

**62**

level of 300 μg kg<sup>−</sup><sup>1</sup>

concentration of 8 g L<sup>−</sup><sup>1</sup> nano-SiO2 for a percentage of 22.16%. The same concentration increased the fresh weight of seedlings by 116.58% and seedlings dry weight by 117.46% compared to control, with an important action upon root and shoot growth. Nano-SiO2 amplified various factors of the growth and conditions of seedlings, i.e. height, diameter of root collar, main length of roots, seedlings lateral root number as well as induction of chlorophyll synthesis. Under abiotic stress nano-SiO2 increases seeds germination in tomato [76] and in saline conditions nano-SiO2 maximized the fresh and dry weight of leaves confirmed that the increment in the proline accumulation, unattached amino-acids, nutrient quantity and antioxidant activity of enzymes increased plant's level of endurance to environmental stress [77]. The chlorophyll content developed on nano-SiO2 treated plants grown in salt-stressed conditions, the application of 1 mM silicon dioxide could alleviate the side effect of salt stress on percentage of germination, length, of root and shoot, weight of seedling, mean germination rate see vigor index and cotyledon reserve mobilization of *Lens culinaris* [78]. Nano silicon dioxide developed the growth of the plant, net rate photosynthesis, level of transpiration, conductance of stomata, rate electron transport and photochemical quell [79].

Regarding the nanotoxicity of nanoparticles action, the involved mechanism is not entirely understand, this mechanism is assumed in the sense by the changes related to the chemical structure, particles size and active surface area of nanoparticles. It is stated [80] that the toxicity action is focused on two directions: i.e. (a) a chemical toxicity based on the chemical composition as the released of toxic ions and (b) stress or stimuli caused by the surface, size or shape of particles. As viewed from chemical physics processes, the solubility of oxide nanoparticles affects the cell culture response and nanoparticle mediated toxicity is partly explained by the release of dissolved components of them [81]. In comparison to metal toxicity in plants and animals, the nanoparticles pathway is different, a problem solved by the introduction of different parameters in experimental tests to evaluate the nanoparticles dynamics. In a plant culture exposed to nanoparticles, the gain and losses related to the development, growth and productivity are not exclusively part of nanoparticles effect but they can be viewed as a participation of the primary ions to biological processes active in plants. Regarding the presence of nanoparticles in soil, as culture area for plants, had to be considered the interaction with the microorganisms in soil because they can positively interact with plants e.g. arbuscular mycorrhizal fungi [80]. The nanoparticles interaction with plants e.g. accumulation in plant biomass affects their fate and transport in the environment. There exists a first report [82] in 2007 regarding the negative effects of nanoparticles upon several plants as corn, cucumber, soybean, cabbage and carrot at relatively low dosage. At microscopic scale, the analysis of the chromosome morphology showed a relation between increased number of aberrations and the increased concentration of nanoparticles e.g. the appearance of stick chromosomes [83]. The phyto-toxicity was observed at molecular and nuclear cell level because the occurrence of stick chromosomes might be related to the degradation or de-polymerization of chromosomal DNA [80]. The extended development of modern agriculture brings besides some true benefits regarding crop productivity increasing problems related to environmental contamination with toxic elements e.g. metals or pesticides compounds and from this point of view nanoparticles used can aggravate the situation. The process of heavy metals accumulation by plants is related for the large majority of plants to roots accumulation and only a small part is translocated to the aboveground of the plants [84]. There are evidence [85] to a translocation process from the roots to the fruits, without the existence of changes due to biochemical processes. It is important to note that the concentration, plant organ or tissue, exposure rate, elemental form, plant species, exposure dosage (chronic/acute) affects the plant

response and in particular the distinct stress response. This is the reason why the complex process of utilization nanoparticles in agriculture has to be monitored to a level that avoids further environmental contamination i.e. soil, water and air.
